1. Field of the Invention
This invention relates to systems for positioning saws in a sawmill and, more particularly, to saw positioning system utilizing digital feedback techniques to accurately measure the saw position and compare it to a precisely selected, desired position to produce a corrective saw positioning signal.
2. Description of the Prior Art
In the art of transforming logs into usable lumber, logs are first sawed into large rectangular boards called cants. The cants are then sent to an edger to be trimmed of waste wood and cut into a plurality of boards. The edger usually comprises a number of saw blades rotating on a common shaft. Means are provided for adjusting the position of each saw to obtain boards of any desired width. A serious disadvantage of prior art edgers results from the fact that the saw blades are not independently adjustable. That is, to vary the width of a board, the position of one saw blade is adjusted. In doing so, the width of the neighboring board is also, of necessity, modified. Using prior art edgers, the sawmill operator initially selects the desired board sizes. The operator will usually find either that the combination of board sizes selected is too wide for the cant or that the combination is too narrow, thereby leaving waste wood at the edge of the cant which is not commercially usable. The operator will then modify the combination of board sizes in an attempt to reduce the quantity of wasted wood. Using prior art edgers, this is a very time-consuming task since each saw must be independently adjusted. The usual practice in sidewalls is to attempt a compromise between wasting an excess amount of wood and wasting an excess amount of time. However, with the increasing scarcity of wood and the increasing cost of labor, both alternatives of this compromise have become unacceptable.